ProjectSummary?Project4 Melanomaisthedeadliestformofskincancer.Whilesignificantprogresshasbeenmadetreatingmelanoma, drug resistant represents one of the greatest challenges to achieve optimal responses and improve patient outcomes. Our long-term goal is to understand mechanisms underlying dysregulated signaling and drug resistance in melanoma to form the pre-clinical basis for improved treatment options. In this project, we are focusing on a clinical unmet need, the treatment of cutaneous melanomas that are wild-type (WT) for BRAF (both WT BRAF/WT NRAS and mutant NRAS). MEK-ERK1/2 signaling is activated in WT BRAF melanoma but the response to MEK inhibitors is poor. Furthermore, immune checkpoint agents elicit responses in only 30-40% of cases and patients who are non-responsive have no effective treatment options. The goals of this project are to identify drugtolerance mechanisms in subsetsof WTBRAF melanomas to provide the basis for new strategies to improve targeted inhibitor treatments and provide salvage options for melanomas that are non-responsive to immune checkpoint agents. Our preliminary data indicate that MEK inhibition triggers a receptor tyrosine kinase-mediated adaptive response in WT/WT melanoma. Based on these data, we hypothesize that the efficacy of MEK inhibitors will be improved with agents targeting either adaptive ErbB3 responses or epigenetic BET/BRD ?reader? proteins, as these epigenetic readers regulate multiple receptor kinasetyrosinekinaseandoncogenicpathwaysassociatedwithdrugresistance.Weaimtoidentifyandtarget mechanisms underlying enhanced activation of the growth factor receptor, ErbB3, in MEK inhibitor-treated melanoma. Additionally, we will test the efficacy of BET inhibitor-based combinations to mitigate stress/therapytolerancemechanismsanddevelopoptimalcombinatorialapproachestooffsetdrugresistance. We will primarily focus on WT/WT melanomabut, where possible, extend our observation to mutant NRAS melanoma. To achieve these goals, we will leverage our unique genetically and clinically annotated models including in vitro 3D/T cell autologous organoids, immune checkpoint inhibitor-resistant patient-derived xenografts and syngeneic mouse models. Through synergistic interactions withother projects and cores in the P01, we will identify mechanisms underlying tumor cell intrinsic and stromal-mediated adaptive responses to targeted and immune therapy and inform future combinatorial targeted/epigenetic inhibitor strategies that can be translated into effective treatments. This project meets the NCI mission by conducting research into the treatmentofthedeadliestformofskincancer.